The present invention relates generally to storage of granular materials and, more specifically, to a method and apparatus for providing low cost storage facilities for grain to prevent deterioration during substantial periods of storage.
In all areas of the world in which grain is produced, there is a need for substantial storage facilities. Because of the large amounts of grain that are harvested over a short period of time, it is desirable to store the grain for varying periods of time before it is used or shipped to market. The nature of grain is such that it may be stored for several years at ambient temperature as long as it is kept dry and well ventilated or aerated. One of the common types of grain storage facility that has evolved has a generally conical form including a protective cover and means for circulating air continuously through the grain to prevent heat build-up and to maintain constant or reduce the moisture content. There have been many different approaches to the problem of aeration of all of the volume of stored grain. If portions of the grain are not aerated, "dead spots" will result where the temperature will increase, allowing insect activity and rotting of the grain.
Many of the storage facilities have been constructed with storage capacities of two million bushels of grain. Although there are cost advantages associated with large grain storage facilities, there are also some disadvantages. As the volume and weight of grain increases, it becomes more difficult to effectively aerate all the grain being contained in the facility. It has also been found that the structural requirements for such large grain storage facilities present erection problems in many areas of the world.
In many countries, there are serious transportation limitations that have resulted in huge quantities of grain rotting before it could be shipped to market or to any sort of grain storage facility. In such countries the farms are often in remote locations and there are not adequate rail or truck transportation means for the farmer to ship his harvested grain to a storage facility before it deteriorates as a consequence of being exposed to the weather. There is a definite need in the countries for a low cost grain storage facility which would be available locally in situations where there is not adequate transportation to ship to a large central storage facility.
A further problem encountered when attempting to provide adequate grain storage relates to the lack of construction equipment available in rural areas of many countries. The typical grain storage facility includes a large aeration tower, requiring a large crane to erect it. In addition, the grain delivery or conveyor system is usually large and cumbersome, requiring a crane for lifting it into place. The foundation for such storage facilities requires substantial quantities of concrete normally not available in remote rural locations. Accordingly, there is a need for a low cost grain storage facility which could be erected without the use of special construction equipment and which would not require large amounts of concrete for a foundation.
The typical prior art grain storage facilities have flexible conical covers to enclose and protect the grain. Examples of these designs are disclosed in the Wolstenholme U.S. Pat. No. 4,454,807; Anderson, et al. No. 4,627,333; Carroll No. 4,887,400; and Anderson, et al. No. 4,726,286. The conical configuration is used because the grain may be piled in this configuration without use of any structural containment walls. The angle of the conical surface with respect to the horizontal surface is about 22.degree., which is the angle of repose of the stored grain. A circular support foundation, including a circular support floor, is normally provided and the grain is delivered to the center to form the conical pile. A flexible conical cover is provided and the grain is inserted beneath the cover. There is normally a support provided for the cover during and after filling of the facility. In some instances the conical pile of stored grain is used as the support for the cover. In the center of the circular support floor, there may be an aeration tower which is designed to draw air through the grain in a generally radially inward direction and then expel it to the atmosphere. There are other duct arrangements used to provide aeration of the grain, but most of them fail to completely aerate the grain in the area of the central axis of the conical pile of grain. The centrally disposed aeration tower may also provide a convenient support for the conveyor that delivers grain to the center of the pile of grain.
The grain conveyor associated with the storage facility extends radially from the top of the aeration tower to the edge of the support floor where there is a generally cylindrical aeration wall. At the other end of the conveyor there is provided a dump pit or the like where grain is deposited temporarily until picked up by the conveyor, which may be a screw or auger type conveyor. At the inner end of the conveyor, a chute of some sort receives the grain and distributes it around the axis of the aeration tower to form the conical pile. The conveyor spans a substantial distance from the edge to the center of the storage facility and is therefore provided with structural support bracing and normally requires a crane to lift it into place.
In order to provide adequate air for aeration of the grain, there are normally provided large motor driven blowers that are located around the periphery of the circular support floor. With the blowers located at the periphery and the air being drawn into the aeration tower, it is necessary to provide a duct from the base of the aeration tower to the air blowers. Thus, the air is drawn radially inwardly through the aeration wall and through the grain pile to the centrally disposed aeration tower, where it is drawn downwardly and then outwardly to the blower. The aeration wall lies along the outer periphery of the conical storage facility and is angled outwardly and provided with air inlet openings which limit the entrance of rain or snow with the air being circulated through the grain.
The storage facility will accommodate for storage on the order of 2 million bushels of grain necessitating good local transportation to bring the grain from the farm to the storage facility. Such good transportation is often not available in remote regions of many countries. Because of the massive size of the grain piles in these storage facilities, there are large pressures compacting the grain at the bottom of these piles. This condition makes proper aeration of the grain difficult and requires that grain supplied to such facilities have low moisture content, i.e., 16% or less. In order to achieve the desired moisture content level, grain dryers are frequently employed. Once the grain has been dried in a grain dryer, the large capacity grain storage facilities described above aerate the grain adequately to prevent deterioration in storage. However, these countries generally have no grain dryers other than air drying the grain in the sun if the weather permits. For use in such countries, it would be desirable to have grain storage facilities that could provide a high level of aeration that would permit storage of high moisture content grain without deterioration of the grain. Particularly, it would be desirable to provide a level of aeration in a grain storage facility that would permit storage of recently harvested grain, and which would dry and reduce the moisture level during the storage period.
In those areas where grain dryers are not readily available to dry the grain prior to storage, the moisture content of the grain may be in the range of 15 to 20 percent moisture; whereas, where dryers are available the grain is usually stored with only 12 to 14 percent moisture. The amount of drying accomplished within the storage facility depends on the grain involved and the ambient conditions. The cleanliness of the grain can also be a significant factor. In arid regions, the grain dries faster than in humid regions; and in cold weather areas, moisture may be sublimated thereby reducing the moisture content of the stored grain. As will be explained, the preferred method and apparatus not only store the grain but also reduce its moisture content substantially when the grain is stored without first being dried.
The above-described grain storage facility, which is typical of those being erected and used, is expensive and complicated to erect, requiring materials and construction equipment that may not be available in some regions of many countries. It would also be desirable to provide a grain storage apparatus which could be easily shipped to a remote site and could be erected using only manual labor and no special construction equipment such as cranes and the like.